An RF ID tag with a battery power supply or of an active type, which is attached to a merchandise article or the like, or carried by a person, transmits an RF signal at a predetermined frequency that carries an ID and other information related to the article or the person, so that the RF signal is received and the information is read out by a reader device. The read-out information is further processed by a computer or the like, so that the distribution of the article or the motion of the person is monitored and managed. The active-type RF ID tag with battery power supply has a larger communication range than a passive-type RF ID tag that receives power from a reader/writer device in a contactless manner, and hence the active-type RF ID tag is practical in use. However, the active-type RF ID tag transmits an RF signal in a fixed cycle, has a risk of being tracked by a third party, and hence has a problem in the security. To address this security problem, there has been developed an improved active-type RF ID tag that responds only to a tag ID request transmitted by the reader/writer device.
PCT International Publication WO 97/43740 published on Nov. 20, 1997 describes radio frequencies identification device which includes an integrated circuit including a receiver, a transmitter and a microprocessor. The receiver and transmitter together form an active transponder. The integrated circuit is preferably a monolithic single die integrated circuit including the receiver, the transmitter and the microprocessor. Because the device includes an active transponder, instead of a transponder which relies on magnetic coupling for power, the device has a much larger range.
Japanese Patent Application Publication JP 2000-113130-A published on Apr. 21, 2000 describes an IC tag detection system with low power consumption. This system includes a plurality of IC tags provided with different set times of day. Each IC tag includes a communication circuit, a control unit, a power source unit for supplying power from a battery to them, and time measuring means. Each IC tag performs transmission at each prescribed set time of day. This system also includes a detector for detecting the presence or absence of the IC tags based on the communication with them. The detector has a communication circuit, and determines the presence or absence of reception from them successively at the respective set times of day of the respective IC tags. Since the IC tag receives no inquiry from the detector, the IC tag can avoid useless reaction and battery consumption.
Japanese Patent Application Publication JP 2001-251210-A published on Sep. 14, 2001 describes a method of locking a frequency in a transmitter at each of two nodes in a full duplex link, without using a separate reference oscillator in each node. The method provides locking of transmission frequencies of both nodes in a full duplex link at the same time by utilizing information of a received frequency to tune carrier frequencies of the transmitters. The offset of the carrier frequency of the first transmitter is detected as the offset of a second corresponding receiver. The second receiver shifts the carrier frequency of the second transmitter, in response to the detected offset, to inform the first transmitter about the detected offset. The first receiver uses the detected offset to correct the carrier frequency of the first transmitter.
Japanese Patent Application Publication JP HEI 10-187898-A published on Jul. 21, 1998 describes an IC card. This IC card transmits and receives data to and from another IC card via an information processing apparatus, to which the IC card may be attached. The IC card has a status setting means for determining the mode identification information from the transmitting data and setting its own operating state in an operation mode that is set by the opposite party, and a mode information transmitting means for selecting the mode information out of a mode information table and adds it to the transmitting data. Then the mode information added by the means is transmitted as the mode identification information together with the transmitting data in a command column or a response column of a transmission mode when the master/slave relation is set or changed. Thus data can be transferred mainly on an IC card and various processing functions can be added to the IC card.
PCT International Publication WO 2004/036482 published on Apr. 29, 2004 describes a system and a method for minimizing the unwanted re-negotiation of passive RF ID tags. Each RF ID tag stores a confirmed read flag to indicate whether that RF ID tag has been previously read. During subsequent interrogations of the tag population, a reader has capability to address all RF ID tags in a tag population or to address only unread RF ID tags. When addressing all RF ID tags, the reader sends a symbol causing all RF ID tags to ignore their confirmed read flag value. Each RF ID tag may also clear its confirmed read flag when this symbol is received. When addressing only unread RF ID tags, the reader sends a symbol causing each RF ID tag to evaluate its confirmed read flag value. Those RF ID tags that have a confirmed read flag value indicating “read” will enter dormant state and will not be re-negotiated. Those RF ID tags that have a confirmed read flag value indicating “not read” will continue to communicate with the reader.
Japanese Patent Application Publication JP 2006-23962-A published on Jan. 26, 2006 describes a contactless IC tag system. In this system, a plurality of IC tags are classified into a master IC tag and slave IC tags. A memory configuration management area in a memory of the master IC tag stores memory configuration information (identification information, a memory head address and a memory byte number of each the IC tag) of the master IC tag itself and the slave IC tags. A reader/writer specifies the master IC tag and handles a group of the IC tags. Thus, large data can be handled efficiently, using a mass-produced low-cost non-contact IC tag having small memory capacity.